The French interior minister says that four people have been killed, including two firefighters, in the Paris bakery blast.

Dozens of people, including several who are in a critical condition, have been injured in the blast that was apparently caused by a gas leak, officials say.

Firefighters tends to a wounded person near the site of a gas leak explosion in Paris. Photo: AP/Kamil Zihnioglu

Firefighters pulled injured victims out of windows and evacuated residents as smoke billowed over Rue de Trevise in the 9th arrondissement of north-central Paris.

Paris prosecutor Remy Heitz said that the cause appears to be an accidental gas leak. He said that Paris firefighters were already at the scene to investigate a suspected gas leak at the bakery when the explosion happened.

An investigation was opened to determine the exact cause of the blast, he said.

Witnesses described the overwhelming sound of the blast and people trapped inside nearby buildings.

Charred debris and broken glass covered the pavement around the apartment building housing the bakery, which resembled a blackened carcass.

Interior Minister Christophe Castaner said “the situation is under control”. After visiting the scene, he described his “shock” at seeing the damage, and said around 200 firefighters and police were involved in the operation.Firefighters work at the scene of a gas leak explosion in Paris (Kamil Zihnioglu/AP)

A helicopter landed in the area to evacuate the wounded. Silver-helmeted firefighters and red fire engines filled the street and inspected adjoining courtyards. A vehicle from gas company GRDF was stationed nearby.

Pedro Goncalves, an employee at the Hotel Mercure opposite the bakery, said he saw firefighters enter the bakery in the morning but he and his co-workers “thought maybe it’s a joke, a false alarm” and they went back to work. About an hour later, he said a blast rocked the surrounding streets.

“In the middle of nothing, I heard one big explosion and then a lot of pressure came at me (and) a lot of black smoke and glass,” he said. “And I had just enough time to get down and cover myself and protect my head.”

Mr Goncalves said he “felt a lot of things fall on me” and that he was struck by shattered glass. He had a few cuts on his head, and spots of blood on his sweater and shirt.A rescue helicopter stands ready to evacuate wounded people (Thibault Camus/AP)

“Thank god I’m OK,” he said, saying that the blast was so powerful that he heard whistling in his ears in the aftermath.

Mr Goncalves said that he ran for the exit and then went to check on the hotel’s clients, adding that some of them had head injuries and were bleeding. He said that the hotel was “destroyed” in the blast.

Another witness told reporters that she was awakened by the blast, and feared it was another terrorist attack.

The bakery is around the corner from the Folies-Bergere theater and not far from the shopping district that includes the famed headquarters of Galeries Lafayette.

The explosion came as the French capital is on edge and under heavy security for yellow vest protests around the country.

A powerful explosion and fire apparently caused by a gas leak at a Paris bakery has injured several people, blasted out windows and overturned cars, police said.

Firefighters work at the scene. Photo: AP/Kamil Zihnioglu

Firefighters pulled injured victims out of windows and evacuated residents as smoke billowed out of the building on Rue de Trevise in the 9th arrondissement of north-central Paris.

Witnesses described on French television the overwhelming sound of the blast and people trapped inside nearby buildings.

A Paris police spokeswoman said several injuries have been reported to police, but no deaths.

Distressing images coming out of central #Paris - huge explosion at a bakery cafe on a Saturday morning. Early reports it may have been caused by gas leak. More info to come. pic.twitter.com/D68oh8I4bB— Trent Murray (@trent_murray) January 12, 2019